U.S. patent number 4,104,320 [Application Number 05/718,584] was granted by the patent office on 1978-08-01 for method of dehydrocyclizing aliphatic hydrocarbons.
This patent grant is currently assigned to Elf-Union. Invention is credited to Jean Rene Bernard, Jean Nury.
United States Patent |
4,104,320 |
Bernard , et al. |
August 1, 1978 |
Method of dehydrocyclizing aliphatic hydrocarbons
Abstract
This invention relates to a method of dehydrocyclizing aliphatic
hydrocarbons to form corresponding aromatic hydrocarbons. According
to the invention, a batch of aliphatic hydrocarbons, in the
presence of hydrogen at a temperature of 430.degree. to 550.degree.
C is passed over a catalyst consisting essentially of a type L
zeolite having exchangeable cations of which at least 90% are
alkali metal ions selected from the group consisting of ions of
sodium, lithium, potassium, rubidium and caesium and containing at
least one metal selected from the group which consists of metals of
groups VIII of the periodic table of elements, tin and germanium,
said metal or metals including at least one metal from group VIII
of said periodic table having a dehydrogenating effect, so as to
convert at least part of the batch into aromatic hydrocarbons. The
aliphatic hydrocarbons preferably contain 6 - 10 carbon atoms.
Inventors: |
Bernard; Jean Rene
(St-Symphorien sur Ozon, FR), Nury; Jean (Caluire,
FR) |
Assignee: |
Elf-Union (Paris,
FR)
|
Family
ID: |
9159829 |
Appl.
No.: |
05/718,584 |
Filed: |
August 30, 1976 |
Foreign Application Priority Data
|
|
|
|
|
Sep 10, 1975 [FR] |
|
|
75 27781 |
|
Current U.S.
Class: |
585/419; 208/141;
208/138 |
Current CPC
Class: |
C07C
5/417 (20130101); B01J 29/60 (20130101); C10G
2400/30 (20130101) |
Current International
Class: |
C07C
5/41 (20060101); B01J 29/60 (20060101); C10G
35/095 (20060101); C10G 35/00 (20060101); B01J
29/00 (20060101); C07C 5/00 (20060101); C07C
015/02 (); B01J 029/28 () |
Field of
Search: |
;260/673.5,673,668D
;208/137,138,140,141 ;423/328,329 ;252/455Z |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gantz; Delbert E.
Assistant Examiner: Schmitkons; G. E.
Attorney, Agent or Firm: Flynn & Frishauf
Claims
We claim:
1. A method of dehydrocyclising non-cyclic aliphatic hydrocarbons,
characterised in that in the presence of hydrogen a batch of the
hydrocarbons is contacted at a temperature of 430.degree. -
550.degree. C with a catalyst consisting essentially of a type L
zeolite having exchangeable cations of which at least 90% are
alkali metal ions selected from the group consisting of ions of
sodium, lithium, potassium, rubidium and caesium and containing at
least one metal selected from the group which consists of metals of
group VIII of the periodic table of elements, tin and germanium,
said metal or metals including at least one metal from group VIII
of said periodic table having a dehydrogenating effect, so as to
convert at least part of the batch into aromatic hydrocarbons.
2. A method according to claim 1, characterised in that the batch
of hydrocarbons comprises paraffins containing 6 - 10 carbon atoms,
preferably normal paraffins.
3. A method according to claim 1, characterised in that the
temperature is between 480.degree. and 520.degree. C.
4. A method according to claim 1, characterised in that the
pressure is from 0 to 40 bars.
5. A method according to claim 1, characterised in that the hourly
liquid spatial velocity of the hydrocarbons is 0.1 to 20
h.sup.-1.
6. A method according to claim 1, characterised in that the molar
ratio of hydrogen to hydrocarbons is between 2 and 20.
7. A method according to claim 1, characterised in that the metal
in group VIII of the periodic table of elements is chosen from the
group consisting of platinum and palladium, and the type L zeolite
contains from 0.1 to 1.5% by weight thereof.
8. A method according to claim 1, characterised in that at least
90% of the exchangeable cations of the L zeolite are ions of at
least one alkali metal chosen from the group consisting of sodium,
lithium, potassium, rubidium and caesium.
9. A method according to claim 8, characterised in that the
exchangeable cations comprise rubidium and/or caesium.
10. A method according to claim 8, characterised in that potassium
ions and caesium ions make up at least 90% of the exchangeable
cations.
11. A method according to claim 8, characterised in that potassium
ions and rubidium ions make up at least 90% of the exchangeable
cations.
12. A method according to claim 9, characterised in that the
caesium ions and/or rubidium ions make up at least 30% of the
exchangeable cations of the L zeolite.
13. A method according to claim 1, characterised in that the L
zeolite contains a metal chosen from the group consisting of
platinum and palladium and also contains a metal chosen from the
group consisting of rhenium, tin, iridium and germanium, in a
proportion such that the total percentage of metals in the zeolite
is between 0.1 and 1.5% by weight.
14. A method according to claim 2, characterised in that the
temperature is between 480.degree. and 520.degree. C.
15. A method according to claim 4, characterised in that the
pressure is from 0 to 25 bars.
16. A method according to claim 15, characterised in that the
pressure is from 0 to 25 bars.
17. A method according to claim 1, characterised in that the hourly
liquid spatial velocity of the hydrocarbons is between 1 and 4.
18. A method according to claim 4, characterised in that the hourly
liquid spatial velocity of the hydrocarbons is between 1 and 4.
19. A method according to claim 1, characterised in that the molar
ratio of hydrogen to hydrocarbons is between 2 and 20.
20. A method according to claim 6, characterised in that the molar
ratio of hydrogen to hydrocarbons is between 3 and 10.
21. A method according to claim 6, characterised in that the metal
in group VIII of the periodic table of elements is chosen from the
group consisting of platinum and palladium, and the type L zeolite
contains from 0.1 to 1.5% by weight thereof.
22. A method according to claim 7, characterised in that at least
90% of the exchangeable cations of the L zeolite are ions of at
least one alkali metal chosen from the group consisting of sodium,
lithium, potassium, rubidium and caesium.
23. A method according to claim 10, characterised in that the
potassium ions and/or caesium ions make up at least 30% of the
exchangeable ions of the L zeolite.
24. A method according to claim 11, characterised in that the
potassium ions and/or rubidium ions make up at least 30% of the
exchangeable ions of the L zeolite.
25. A method according to claim 1, characterised in that the L
zeolite contains a metal chosen from the group consisting of
rhenium, tin, iridium and germanium, and also contains a metal
other than rhenium and iridium chosen from metals of group VIII of
the periodic table of elements, in a proportion such that the total
percentage of metals in the zeolite is between 0.1 and 1.5% by
weight.
Description
The invention relates to a method of dehydrocyclising aliphatic
hydrocarbons, more particularly batches of hydrocarbons comprising
paraffins containing 6 to 10 carbon atoms, to form the
corresponding aromatic hydrocarbons.
This reaction, called "reforming," is conventionally used in the
oil industry for converting normal paraffins (which are undesirable
constituents in petrol owing to their very low octane number) into
aromatic components having a high octane number, which are suitable
as fuels and also have many other petrochemical uses, e.g. as
solvents, etc.
The conventional methods of performing these dehydrocyclisation
reactions are based on the use of catalysts comprising a noble
metal on a carrier. Known catalysts of this kind are based on
alumina carrying from 0.2 to 0.8% by weight of platinum and a
second auxiliary metal.
The possibility of using carriers other than alumina has also been
studied and it has been proposed to use certain molecular sieves
such as X and Y zeolites, which are suitable provided that the
reactants and products are sufficiently small to flow in the pores
of the zeolite.
In the conventional method of carrying out the aforementioned
dehydrocyclisation, a batch of hydrocarbons to be converted is
passed over the catalyst, in the presence of hydrogen, at
temperatures of the order of 500.degree. C and pressures varying
from 5 to 30 bars. Part of the injected batch is converted into
aromatic hydrocarbons by dehydrocyclisation, but the reaction is
accompanied by isomerization and cracking reactions which also
convert the paraffins into isoparaffins and lighter
hydrocarbons.
The rate of conversion of the hydrocarbon batch into aromatic
hydrocarbons varies with the reaction conditions and the nature of
the catalyst.
The catalysts hitherto used have given satisfactory results but it
has been discovered that catalysts based on L zeolite are more
selective with regard to the dehydrocyclisation reaction and can be
used to improve the rate of conversion to aromatic hydrocarbons
without requiring higher temperatures and lower pressures, which
usually have a considerable adverse effect on the stability of the
catalyst.
To this end, the invention provides a method of dehydrocyclising
aliphatic hydrocarbons, characterised in that a batch of the
hydrocarbons is contacted in the presence of hydrogen at a
temperature of 430.degree. - 550.degree. C with a catalyst
consisting essentially of a type L zeolite having exchangeable
cations of which at least 90% are alkali metal ions selected from
the group consisting of ions of sodium, lithium, potassium,
rubidium and caesium and containing at least one metal selected
from the group which consists of metals of group VIII of the
periodic table of elements, tin and germanium, said metal or metals
including at least one metal from group VIII of said periodic table
having a dehydrogenating effect, so as to convert at least part of
the batch into aromatic hydrocarbons.
In this method, the use of L zeolite-based catalysts is very
advantageous since these catalysts are very efficient with regard
to dehydrocyclisation and are both more selective and more stable
than known catalysts.
In the method according to the invention, the batch of hydrocarbons
preferably comprises paraffins containing 6 to 10 carbon atoms,
preferably normal paraffins.
This hydrocyclisation is carried out in the presence of hydrogen at
a pressure adjusted so as to favour the reaction thermodynamically
and limit undesirable hydro-cracking reactions by kinetic means.
The pressures used vary from 0 to 40 bars, preferably from 0 to 25
bars, the molar ratio of hydrogen to hydrocarbons being between 2
to 20, preferably between 3 and 10.
In the temperature range from 430.degree. to 550.degree. C the
dehydrocyclisation reaction occurs with acceptable speed and
selectivity.
If the operating temperature is below 430.degree. C, the reaction
speed is insufficient and consequently the yield is too low for
industrial purposes. When the operating temperature is high,
approximately 550.degree. C, and although the speed of the
dehydrocyclisation reaction is high, interfering secondary
reactions such as hydro-cracking and coking occur, and
substantially reduce the yield. It is not advisable, therefore, to
exceed the temperature of 550.degree. C.
The preferred temperature range (450.degree. - 550.degree. C) is
that in which the process is optimum with regard to activity,
selectivity and the stability of the catalyst.
The hourly liquid spatial velocity of the hydrocarbons, in
accordance with the feed rate, is between 0.1 and 20 h.sup.-1,
preferably between 1 and 4.
The catalyst according to the invention is a type L zeolite charged
with one or more dehydrogenating constituents.
L type zeolites are synthetic zeolites such as chabazite and
crystallise in the hexagonal system. A theoretical formula is
M.sub.9 /n [(AlO.sub.2).sub.9 (SiO.sub.2).sub.27 ] in which M is a
cation having the valency n.
The real formula may vary without changing the crystalline
structure; for example the ratio of silicon to aluminium may vary
from 2.5 to 3.5.
A more complete description of these zeolites is given e.g. in U.S.
Pat. No. 3,216,789 which, more particularly, gives a conventional
description of these zeolites with respect to their X-ray
diffraction spectrum. The zeolites occur in the form of cylindrical
crystals a few hundred Angstroms in diameter and have
channel-shaped pores.
The hydrocarbon sorption pores are channels parallel to the
cylinder axis and between 7 and 8 A in diameter.
L zeolites are conventionally synthesized in the potassium form --
i.e. in the theoretical formula given previously, most of the M
cations are potassium. The M cations are exchangeable, so that a
given L zeolite, e.g. an L zeolite in the potassium form, can be
used to obtain L zeolites containing other cations, by subjecting
the L zeolite to ion exchange treatment in an aqueous solution of
appropriate salts. However, it is difficult to exchange more than
80% of the original cation, e.g. potassium, since some exchangeable
cations in the zeolite are in sites which are difficult for the
reagents to reach.
In the method according to the invention, the catalyst carrier is
advantageously an L zeolite in which at least 90% of the
exchangeable cations are ions of at least one alkali metal chosen
from the group comprising potassium, lithium, sodium, rubidium and
caesium.
In a preferred embodiment, an L zeolite is used in which the
exchangeable cations comprise, for example, caesium ions and/or
rubidium ions. In the latter case, the caesium and/or rubidium ions
preferably make up at least 30% of the exchangeable cations of the
L zeolite.
As previously explained, an L zeolite of the aforementioned kind
can be obtained from an L zeolite in the potassium form by
subjecting it to ion exchange by treatment with an aqueous solution
containing a rubidium or caesium salt, after which the zeolite is
washed so as to eliminate excess ions.
The rate of exchange can be increased by repeated ion exchange
treatment of the zeolite. Since, however, it is difficult to
exchange more than 80% of the original cation in the final product,
the process yields an L zeolite in which at least 90% of the
exchangeable cations are potassium ions and rubidium or caesium
ions.
The generally accepted theory relating to the dehydrocylisation of
paraffins refers to acid sites in which the olefins formed by
dehydrogenation of paraffins are cyclised. By contrast, in the
method according to the invention, the L zeolites used are neutral,
i.e. have not been exchanged with either hydrogen or ammonium ions
capable of producing hydrogen ions or with multivalent cations
which make zeolites somewhat acid.
The catalyst carriers according to the invention are charged with
one or more dehydrogenating constituent metals from group VIII of
the periodic table of elements, e.g. nickel, ruthenium, rhodium,
palladium, iridium or platinum.
The preferred substances are palladium and particularly platinum,
which are more selective with regard to dehydrocyclisation and are
also more stable under the dehydrocyclisation treatment
conditions.
The preferred percentage of platinum in the catalyst is between 0.1
and 1.5%, the lower limit corresponding to minimum catalyst
activity and the upper limit to maximum activity; this allows for
the high price of platinum, which does not justify using a higher
quantity of the metal since the result is only a slight improvement
in catalyst activity.
In order to improve the stability of the catalyst, another metal
such as rhenium, iridium, tin or germanium is preferably introduced
at the same time as platinum and/or palladium, the quantity of the
other metal being such that the total percentage of metals in the
zeolite is from 0.1 to 1.5% by weight. In this manner a reduction
can also be made in the percentage of platinum or palladium without
affecting the activity of the catalyst.
Metals are introduced into the L zeolite by impregnation or
exchange in an aqueous solution of appropriate salt. When it is
desired to introduce two metals into the zeolite, the operation is
carried out simultaneously, using a solution of salts of both
metals.
By way of example, platinum can be introduced by impregnating the
zeolite with an aqueous solution of chloroplatinic acid,
choroplatinuous acid, dinitrodiamino-platinum or tetramminoplatinum
chloride. In an ion exchange process, platinum can be introduced by
using cationic platinum complexes such as tetramminoplatinum
chloride.
Similar compounds can be used for iridium, and perrhenic acid for
rhenium.
After the desired metal or metals have been introduced, the
catalyst is calcined in air and then reduced in hydrogen.
At this stage it is ready for use in the dehydrocyclisation
process. In some cases however, for example when the metal or
metals have been introduced by an ion exchange process, it is
preferably to eliminate any residual acidity of the zeolite by
heating the catalyst with an aqueous solution of an alkaline base
such as sodium carbonate in order to neutralise any hydrogen ions
formed during the reduction of metal ions by hydrogen.
In other cases, the catalyst can be sulphurated so as to reduce the
hydro-cracking reactions, which are always more prominent at the
beginning of the hydrocyclisation.
By way of example, a catalyst based on L zeolite in the potassium
form containing 0.9% platinum was prepared as follows:
5 g of L zeolite in the potassium form was calcined at 480.degree.
C for 3 hours. The resulting solid was impregnated with a solution
of 0.09 g diammino platinum chloride in 5 ml water.
The impregnated solid was left at ambient temperature for 30
minutes, then dried in an oven at 100.degree. C.
The resulting catalyst was calcined for 3 hours at 480.degree. C in
a stream of dry air. It was found by analysis to contain 0.5%
platinum.
It was then placed in a dynamic catalytic reactor and reduced in a
stream of hydrogen at 510.degree. C.
If it is desired to neutralize the residual acidity of the zeolite,
the catalyst after reduction is processed with 50 ml of 0.1 N
sodium carbonate at 50.degree. C for 24 hours.
As a second example, a catalyst containing platinum and comprising
rubidium or caesium as the exchangeable cation of the zeolite was
prepared as follows: 10 g of L zeolite in the potassium form was
contacted with 100 ml of a solution containing 2 mols pf rubidium
chloride per liter. The mixture was agitated and boiled for 3
hours; the solid was then filtered and washed until the chloride
ions had disappeared. The operation was repeated once.
An L zeolite containing caesium can be obtained simply by using
caesium chloride instead of rubidium chloride in the preceding
process. In the case of rubidium, the carrier contains 21% by
weight of the metal; in the case of caesium, it contains 23% by
weight of the last-mentioned alkaline metal. The rates of exchange
are 70% and 49% respectively; the remaining cations are the
original potassium.
The resulting carriers are impregnated with an aqueous solution of
tetramminoplatinum chloride so as to deposit 0.6% by weight of
platinum. The mixture is left to mature at ambient temperature for
30 minutes, after which the catalyst is dried in an oven at
110.degree. C and finally calcined for 3 hours at 480.degree. C in
a stream of dry air.
The previously-described catalysts can be used for dehydrocyclising
any batch of hydrocarbons containing paraffins with 6 - 10 carbon
atoms, more particularly normal paraffins and isoparaffins
containing a straight chain of at least 6 carbon atoms.
The dehydrocyclisation reaction is carried out by injecting one of
the batches in the presence of hydrogen into a dynamic reactor
after the chosen catalyst has been introduced therein.
The invention will be more clearly understood from the following
non-limitative examples which are given so as to illustrate the
method according to the invention, applied to the
dehydrocyclisation of normal hexane.
EXAMPLES 1 to 6
In these examples, a dynamic reactor was used at atmospheric
pressure. In all the examples, 0.6 g of catalyst was placed in the
reactor and reduced at 510.degree. C in a stream of hydrogen. Next,
a mixture of normal hexane and hydrogen was sent over the catalyst,
the molar ratio of hydrogen to N-hexane being 6. The total hourly
spatial velocity of the gases was 1500 h.sup.-1. After the catalyst
had been in operation for an hour, the hydrocarbon effluents were
analysed by flame ionization chromatography. The conditions and
results of examples 1 to 6 are shown in Table 1, in which the last
4 columns represent the percentages by weight of hydrocarbons in
the analysed effluents. In the columns, "light products" denote
hydrocarbons containing less than 6 carbon atoms and branched
isomers of hexane; "hexanes" denote not only C.sub.6 olefins but
also methylcyclopentane. The "aromatics" mainly consist of
benzene.
TABLE I ______________________________________ % % n Light % Temp.
Hex- Pro- Hex- % Ex. Catalyst .degree. C ane ducts anes Aromatics
______________________________________ 1 0.9% Pt/KL prepared
490.degree. C 2.2 4.09 1.6 92.2 by impreg- nation 2 " 460.degree. C
47.1 3.4 9.25 40.3 3 0.8% Pt/KL prepared by 460.degree. C 52 7.8
4.2 36 exchange 4 " Treatment with 0.1 N NaHCO.sub.3 460.degree. C
50.1 2.1 8.3 38.8 after reduction 5 0.3% Pt, 0.05% Ir/KL prepared
460.degree. C 53 2.1 8.6 36.3 by impreg- nation 6 0.8% Pt/NaL
prepared 460.degree. C 39.3 3.8 7.2 55.7 by impreg- nation
______________________________________
The catalysts in Examples 1 and 2 were an L zeolite in the
potassium form containing 0.9% platinum and were prepared by
impregnation.
The catalyst in Example 3 was a zeolite in the potassium form
containing 0.8% platinum fixed by ionic exchange.
The catalyst in Example 4 was identical with the catalyst in
Example 3 except that after being reduced with hydrogen it was
neutralized with a solution of 0.1 N sodium carbonate.
The catalyst in Example 5 was an L zeolite in the potassium form
containing 0.3% platinum and 0.05% iridium fixed by
impregnation.
The catalyst in Example 6 was an L zeolite in the potassium form
exchanged with sodium (i.e. containing 2.2 by weight of sodium and
13.1% by weight of potassium) and containing 0.8% platinum fixed by
impregnation.
The results show the efficiency of the catalyst, which gives good
n-hexane conversion rates at temperatures below 500.degree. C with
considerable selectivity for the dehydrocyclisation reaction.
EXAMPLE 7
30 g of the catalyst used in Example 1 was placed in a metal
dynamic reactor and reduced at 510.degree. C with hydrogen. A batch
of normal hexane and hydrogen, the molar ratio of n-hexane to
hydrogen being 6, was sent over the catalyst at a pressure of 10
bars and a liquid hourly spatial velocity of 2.5. When the catalyst
activity was stable, the conversion of n-hexane at 500.degree. C
was 80% and the reaction products contained 21% light products, 29%
n-hexane isomers and 50% aromatics.
EXAMPLES 8 - 10
In these examples, a dynamic reactor was used at atmospheric
pressure. In all the examples, 0.6 g of catalyst was placed in the
reactor and reduced at 510.degree. C in a stream of hydrogen. Next,
a mixture of normal hexane and hydrogen, the molar ratio of
hydrogen to n-hexane being 6, was sent over the catalyst. The total
hourly spatial velocity of the gases was 1500 h.sup.-1, and the
temperature was 460.degree. C. After the catalyst had been in
operation for an hour, the hydrocarbon effluents were analysed by
flame ionisation chromatography.
The reseults of Examples 8 - 10 are shown in Table 2. In this
Table, conversion is defined by the percentage by weight of
hydrocarbons other than n-hexane in the gaseous effluents, and the
selectivity is defined by the percentages by weight of hydrocarbons
obtained in the converted product. The light products are defined
as saturated C.sub.1 - C.sub.5 hydrocarbons and C.sub.2 - C.sub.4
olefins.
The isohexanes are methylpentanes. The same fraction contains
C.sub.5 olefins.
The intermediates comprise C.sub.6 olefins and
methylcyclopentane.
The aromatics mainly comprise benzene, but also contain traces of
toluene and xylene.
A comparison of the results in Examples 8 - 10 shows that catalysts
based on L zeolite containing rubidium or caesium are more active
and more selective than catalysts based on L zeolite in the
potassium form.
TABLE 2 ______________________________________ Selectivity Con-
Light i- ver- Pro- Hex- Inter- Aro- Examples Catalyst sion ducts
ane mediates matics ______________________________________ 8 0.6%
Pt/KL. 50 3 5 13 79 9 0.6% Pt/0.7 73 3 5 6 88 Rb.0.3 KL 10 0.6%
Pt/0.49 71 2 5 8 85 Cs.0.51 KL
______________________________________
* * * * *